License ledger should be isolated as a non fungible token

[3esmit]

Feature Request

In case of upgrade on License.sol, the change of License.sol, the migration would be required. To don't require migrations, isolate the owners of licenses in a separate (probably ERC721) token.

Summary

Licenses would be created by a controlling contract, which contains the logic for how license token is generated or destroyed, but they are stored in chain and managed by the users as a NFT in a dedicated address. The contract managing the sell of licenses would change controller of the NFT on a migration, so the new license market logic would own the token, making the upgrade seamless for existent users and contracts relaying on the verification of this token.

[richard-ramos]

I'm not sure of this enhancement. Under what conditions would a migration be required?
Currently the licenses are handled as a mapping, and to determine if a user has a license, we check if that mapping has a value for the user address. Doing an upgrade should not affect the state of this variable.